The present invention generally relates to track position detecting mechanisms, and more particularly to a track position detecting mechanism of a magnetic disc recording and/or reproducing apparatus for detecting an outermost peripheral track position during an initializing operation of the magnetic disc recording and/or reproducing apparatus.
FIG. 1 shows an example of a conventional track position detecting mechanism used in a magnetic disc recording and/or reproducing apparatus (hereinafter simply referred to as a disc apparatus). A carriage 1 has a magnetic head 2a provided on a base 1a thereof, and a magnetic head 2b which is provided on a lower surface of an upper head arm 3. The carriage 1 engages a lead screw 5 which is driven by a motor 4. Accordingly, the carriage 1 moves in a radial direction X of a magnetic disc (not shown) depending on a rotation quantity of the lead screw 5, and the magnetic heads 2a and 2b make sliding contact with recording surfaces of the magnetic disc. A recording region on the recording surface is defined by an innermost peripheral track and an outermost peripheral track on the magnetic disc. The lead screw 5 penetrates one side portion of the carriage 1 while a guide shaft 6 penetrates the other side portion of the carriage 1. The carriage 1 moves under the guidance of the guide shaft 6.
During an initializing operation of the disc apparatus, it is necessary to detect the outermost peripheral track (track "00") as a reference point. This reference point is used as a reference in determining track positions on the magnetic disc during a recording mode or a reproducing mode of the disc apparatus. This outermost peripheral track is detected when a projecting member 1b which projects upwardly from the base 1a of the carriage 1 enters within a slit 7a of an optical detector 7 and interrupts an optical path within the optical detector 7 between a light emitting element (not shown) and a light receiving element (not shown) which constitute the optical detector 7. The optical detector 7 is mounted on a lower surface of a plate 8 which is indicated by a one-dot chain line and is fixed to a base (not shown) of the disc apparatus. The position of the optical detector 7 is fixed after a relative position between the optical detector 7 and the projecting member lb is appropriately adjusted.
In an initial state of the disc apparatus and when a power failure occurs during operation of the disc apparatus, for example, the magnetic heads 2a and 2b are automatically moved to the outermost peripheral track positions on the respective recording surfaces of the magnetic disc. In the conventional track position detecting mechanism, measures are taken so as to facilitate the loading and unloading of the magnetic disc when the magnetic heads 2a and 2b are located at the outermost peripheral track positions on the respective recording surfaces of the magnetic disc. In other words, a rod 9 moves in a direction Y and makes contact with an arm portion 3a of the upper head arm 3 which is urged downwardly by a torsion spring 10, thereby bending a leaf spring 3b which supports the upper head arm 3 and separating the magnetic head 2b from the magnetic head 2a. When the separation of the magnetic heads 2a and 2b takes place, a force due to a pivotal displacement of the upper head arm 3 acts on the carriage 1 in the upward direction, and a slight resilient deformation occurs in the guide shaft 6. For this reason, the projecting member 1b of the carriage 1 is also slightly inclined or displaced due to the resilient deformation of the guide shaft 6. When the projecting member 1b is slightly inclined or displaced, a timing with which the optical path within the optical detector 7 is interrupted by the projecting member 1b varies slightly, and there is a problem in that an error is introduced in the detection of the outermost peripheral track position. When such an erroneous detection of the outermost peripheral track position occurs, all accesses made during the operating mode of the disc apparatus will be made to an erroneous track position since each access refers to the reference point (that is, the outermost peripheral track position).
For example, it is conceivable to make the diameter of the guide shaft 6 large and make the guide shaft 6 rigid so that the guide shaft 6 will not undergo a resilient deformation even when the above described force acts on the carriage 1. However, in this case, a resistance against a sliding motion of the carriage 1 increases due to the increased outer peripheral surface of the guide shaft 6, and the motor 4 must have a large torque in order to drive the carriage 1. Consequently, the size of the motor 4 increases and there is a problem in that the track position detecting mechanism as a whole becomes bulky because of the large-diameter guide shaft 6 and the large motor 4. It is highly undesirable that the track position detecting mechanism is bulky since the track position detecting mechanism must usually be accommodated within a limited space inside the disc apparatus.
On the other hand, it is also conceivable to use such a rigid material for the guide shaft 6 that no resilient deformation will occur even when the above described force acts on the carriage 1. But at the present, a highly rigid material suited for use in the guide shaft 6 is expensive, and there is no available material that meets the rigidity requirement and is also satisfactory costwise.